1. Field of the Invention
The present invention relates to data storage and, more particularly, to memory cards that provide data storage.
2. Description of the Related Art
Memory cards are commonly used to store digital data for use with various products (e.g., electronics products). Examples of memory cards are flash cards that use Flash type or EEPROM type memory cells to store the data. Flash cards have a relatively small form factor and have been used to store digital data for products such as cameras, hand-held computers, set-top boxes, hand-held or other small audio players/recorders (e.g., MP3 devices), and medical monitors. A major supplier of flash cards is SanDisk Corporation of Sunnyvale, Calif.
A conventional memory system can be represented, for example, by a memory card (e.g., flash card) format. A conventional memory system includes a memory controller and various memory chips. The number of memory chips is dependent upon the storage capacity to be provided by the conventional memory system. The memory controller receives an input voltage (VIN) and an Input/Output (I/O) bus. The memory controller operates to supply an address/data/control bus to each of the memory chips. In addition, the memory controller can produce chip select signals that are provided to chip enable terminals of each of the memory chips. The memory controller uses the chip select signals to selectively activate one of the memory chips that is to be accessed for data storage or retrieval. In addition, since the memory chips require various voltage levels for operation, the memory controller can include a charge pump and regulation circuit. Alternatively, each of the memory chips can themselves include a charge pump and regulation circuit. The charge pump and regulation circuit can produce several different output voltage levels that are supplied to each of the memory chips. As an example, the input voltage (VIN) might be 3.3 or 1.8 Volts and the different output voltage levels might be 3 Volts, 6 Volts, 12 Volts and 24 Volts.
Memory cards are removable storage media that are highly portable due to their relatively small form factor. As previously noted, memory cards have been used to store digital data for products such as cameras, hand-held computers, set-top boxes, hand-held or other small audio players/recorders (e.g., MP3 devices), and medical monitors. These products are also referred to as host devices.
Traditionally, host devices have utilized a file system configuration that supports sixteen bit (16-bit) addressing. The 16-bit addressing was inherited from the popular Disk Operating System (DOS) environment. Unfortunately, the 16-bit addressing has a maximum addressable address space of two (2) gigabytes (GBs). This presents a problem because the data storage capacity of memory cards is, or will soon be, able to exceed two gigabytes. Consequently, host devices using the common 16-bit addressing would be unable to utilize any additional memory capacity provided by the memory card that is beyond two gigabytes.
More recently, some more sophisticated and more costly host devices use a file system configuration that supports more than sixteen bits for each allocation unit or cluster. The FAT-32 is an extension of the 16-bit FAT system that uses twenty-eight of the 32-bit address for each allocation unit or cluster. The maximum addressable address space for such is eight (8) terabytes (TBs). Today and for the foreseeable future, the data capacity of a memory card is well below that of even a single terabyte.
Further, memory cards practically need to be able to be used in either a host device using 16-bit addressing or a host device using 32-bit addressing without damage or loss of existing data. In other words, the memory cards need to operate properly regardless of the file system configuration. However, the presence of two different file system configurations can lead to not only inefficient data storage but also unreliable data storage. The unreliable data storage can even result in a loss of data.
Thus, there is a need for improved approaches to extend capacity of memory cards yet reliably support not only older but also modern file systems.